The airport's security unit later said in a widely publicised document: "According to intelligence sources, there is a specific threat to attack Entebbe International Airport by an unknown terrorist group... Such a threat cannot be taken lightly."

'Stay calm'

Army spokesman Paddy Ankunda said troops had been deployed at the airport and in the capital, about 35km (20 miles) from Entebbe.

"People must be vigilant in the face of this threat, report any suspicious individuals seen in their areas," he said.

He called on people to "stay calm and alert".

A reporter with AFP news agency said there was a heavy security presence in Kampala, with soldiers marching along city streets.

Several international conferences were taking place in the city and the security forces wanted to make sure that visitors were safe, Kampala Metropolitan Police spokesman Patrick Onyango is quoted as saying.